OPA314AIDBVT datasheet(21/53 Pages) TI2

21 / 53 page

OUT

V+

Device

OUT

2pRC

3 dB

R = R

C = C

Q = Peaking factor

(Butterworth Q = 0.707)

G =

(

2 -

OPA314, OPA2314, OPA4314

www.ti.com

SBOS563G – MAY 2011 – REVISED JUNE 2015

Application Information (continued)

Figure 37. Two-Pole Low-Pass Sallen-Key Filter

8.1.2 Capacitive Load and Stability

The OPA2314 device is designed to be used in applications where driving a capacitive load is required. As with

all op-amps, specific instances can occur where the OPA2314 device can become unstable. The particular op-

amp circuit configuration, layout, gain, and output loading are some of the factors to consider when establishing

whether or not an amplifier is stable in operation. An op-amp in the unity-gain (1 V/V) buffer configuration that

drives a capacitive load exhibits a greater tendency to be unstable than an amplifier operated at a higher noise

gain. The capacitive load, in conjunction with the op-amp output resistance, creates a pole within the feedback

loop that degrades the phase margin. The degradation of the phase margin increases as the capacitive loading

increases. When operating in the unity-gain configuration, the OPA2314 device remains stable with a pure

capacitive load up to approximately 1 nF. The equivalent series resistance (ESR) of some very large capacitors

(CL greater than 1 μF) is sufficient to alter the phase characteristics in the feedback loop such that the amplifier

remains stable. Increasing the amplifier closed-loop gain allows the amplifier to drive increasingly larger

capacitance. This increased capability is evident when observing the overshoot response of the amplifier at

higher voltage gains. See the graph, Figure 20.

One technique for increasing the capacitive load drive capability of the amplifier operating in a unity-gain

configuration is to insert a small resistor, typically 10

Ω to 20 Ω, in series with the output, as shown in Figure 38.

This resistor significantly reduces the overshoot and ringing associated with large capacitive loads. One possible

problem with this technique, however, is that a voltage divider is created with the added series resistor and any

resistor connected in parallel with the capacitive load. The voltage divider introduces a gain error at the output

that reduces the output swing.

Figure 38. Improving Capacitive Load Drive

Submit Documentation Feedback

Product Folder Links: OPA314 OPA2314 OPA4314

OPA314AIDBVT Datasheet(PDF) 21 Page - Texas Instruments

OPA314AIDBVT Datasheet(HTML) 21 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53

Datasheet Download

Link URL